The form factors of mobile phones have changed greatly since the development of the original mobile phones. For example, initial mobile phones were often “brick” shaped with a small screen for displaying user input entered via physical buttons. Over time with further development, the sizes of mobile phones shrunk, and new form factors, such as sliding phones and foldable phones, were introduced. A sliding phone or foldable phone utilized a two-piece case with a rigid screen carried by one piece of the case that was capable of moving with respect to the other piece of the case. Eventually, as touch screens replaced the combination of traditional screens with physical buttons, the form factors of mobile phones coalesced around a flat, rectangular shape carrying a rigid touch screen. This form factor has proven highly successful, with nearly all mobile phones sold today having this form factor.
However, as mobile operating systems continue to grow in complexity and capability, and as touch screens continue to increase in resolution, the desire for larger touch screens grows, to the point where many mobile phones sold today have a touch screen that measures over six inches in diagonal. There is a limit to this screen size growth however, namely the fact that many users carry their mobile phones in their pockets. Therefore, mobile phones themselves are somewhat limited in size.
As a solution to this issue, and to permit the size of touch screens to continue to grow while not increasing the size of mobile phones, some manufacturers have begun to develop foldable touch screens, with the aim of creating a foldable mobile phone having a large, foldable singular touch screen. With such foldable mobile phones, one form factor design concern becomes thickness when folded. Therefore, internal space is at a premium. Since a foldable mobile phone should be able to detect screen angle (open, closed, etc.) to provide desirable functions for users such as entry into and exit from sleep states, or display brightness control, with current designs, some of the internal space is unfortunately consumed using sensors such a gyroscopes, hall effect sensors, or optical sensors to detect the panel angle.
Therefore, it would be desirable for there to be hardware and techniques for determining the screen angle or open close detection without the use of such additional sensors. It would be particularly desirable if the screen angle could be determined using hardware that will necessarily be present in every foldable mobile phone with a touch screen, such as by using the touch screen itself to perform the detection.
So as to facilitate the discussion and understanding of the disclosures herein, a background on touch screen technology will now be given.
Touch screens typically operate based on capacitive touch sensing, and include a patterned array of conductive features. For instance, the patterned array of conductive features may include sets of lines, conductive pads, overlapping structures, interleaved structures, diamond structures, lattice structures, and the like. By evaluating changes in capacitance at different lines or sets of lines, a user touch or hover, such as by a finger or stylus, can be detected.
Two common capacitive touch sensing techniques or modes that may be performed on touch screens are mutual capacitance sensing and self capacitance sensing. In a mutual self capacitance sensing mode, shown in FIGS. 1A-1B, a drive signal is applied to a subset of the lines referred to as drive lines, and capacitance values are measured at a subset of the lines referred to as sense lines, with it being understood that the sense lines cross the drive lines in a spaced apart fashion therefrom to form a capacitive touch matrix. Each crossing of drive line and sense line forms a capacitive intersection. This electric field between a drive line and a sense line, in the absence of a touch, can be seen in FIG. 1A.
Since bringing a finger or conductive stylus near the surface of the touch screen changes the local electric field, this causes a reduction in the capacitance between the drive lines and the sense lines (the “mutual” capacitance), and the capacitance change at every individual capacitive intersection can be measured to accurately determine the touch location. This change of electric field due to the presence of a finger can be seen in FIG. 1B, where the finger “steals” charge, and thus the capacitance between the drive line and sense line is reduced.
Since mutual capacitance sensing allows the measuring of each intersection between drive line and sense line individually, the output of mutual capacitance sensing is a two-dimensional matrix of values, with one value for each capacitive intersection (crossing between drive line and sense line). Thus, it can be appreciated that mutual capacitance sensing allows multi-touch operation where multiple fingers or styli can be accurately tracked at the same time.
In a self capacitance sensing mode, shown in FIGS. 2A-2B, the drive signal is applied to every line, regardless of orientation. This application of the drive signal in the absence of a touch can be seen in FIG. 2A. Bringing a finger or conductive stylus near the surface of the touch screen changes the local electric field, as shown in FIG. 2B, increasing the capacitance between the drive line or sense line of interest and ground (the “self capacitance”) in this instance. However, since all lines are driven, the capacitance change cannot be measured on a per capacitive intersection basis. Therefore, the output of self capacitance sensing is two one dimensional arrays of values, with one value for each line.